The computation and memory required by CrossFilter depend on the ResponseDuration, the AllowLongerCapture checkbox, and whether it is Stereo or not (and of course, the sample rate you have selected). To get more of them in parallel, try reducing the ResponseDuration value and check the AllowLongerCapture box. For example, you can get six of them on a Pacarana when you have ResponseDuration set to 1 s.
The resources used by combinations of CrossFilters (or combinations of any Sounds for that matter) is somewhat nonlinear.